Chapter 14, Problem 13QP

Indicate the oxidation number of each element in the following species.

$\begin{array}{l}\left(\text{a}\right)\text{ Cr}\left(s\right)\\ \left(\text{b}\right){\text{ Br}}_{\text{2}}\left(l\right)\\ \left(\text{c}\right){\text{ Cr}}^{\text{3+}}\left(aq\right)\\ \left(\text{d}\right){\text{ Br}}^{-}\left(aq\right)\end{array}$